True-time delay devices based on the White cell are described in U.S. Pat. Nos. 6,525,889, 6,388,815, 6,674,939, 6,724,951, and 7,430,347. True-time delay devices based on the Robert cell are described in U.S. Ser. No. 14/269,857. True-time delay devices based on the Fourier cell are described in U.S. Pat. No. 7,911,671. Further, optical cross-connects based on the White cell are described in U.S. Pat. Nos. 6,266,176, 6,760,140, and 7,660,499, and based on the Fourier cell are described in U.S. Pat. No. 7,630,598. Apparatuses for using a time delay device as an optical correlator are described in U.S. Pat. No. 6,952,306 and monitoring the quality of optical links in U.S. Pat. No. 7,236,238.
The White cell and the Fourier cell are both free-space optical systems in which arrays of light beams make multiple passes and are re-imaged to arrays of light spots multiple times. Each time the spots are re-imaged, they can be made to land on a pixelated optical spatial light modulator (SLM) of some type. The SLM changes some property of the beam landing on each pixel to change the path of that beam. Then, depending on the path a beam takes, some optical operation is performed (or not performed) so as to cause the final state of each output beam to be different in a controllable way.
An example is an optical time-delay device. In this case, the SLM pixel may direct a beam to a “null” path (a path requiring some amount of time to cross the cell and return to the SLM), or to a delay path, in which case the beam takes a specified longer amount of time to return, and, thus, has a delay relative to a beam that took a null path. Another example is an optical cross-connect. Here, a beam may be returned to a location in a row or column that corresponds directly to its initial row or column, or may be “switched” to return to a different row or column.
In both cases, beams make multiple passes through the cell, and on each round trip each beam may be switched again. Generally the operation performed on the beam is different each pass, for example on the first pass the time delay (or row or column shift) may be smaller or larger than that on the second pass. By combining delays or shifts or varying sizes, a wide range of time delays (or row or column shifts) may be implemented.
In what follows, the set of components that perform the switching (the choosing of the operations to be performed) will be referred to as the switching engine. For example, the White cell may be a switching engine. The set of components that performs the desired operation (delay, shifting, et cetera) will be called the “operation part.” For example, the optical delay elements in a time delay device is the time “operation part.”